In the prior art, when a loudspeaker operates with a low-frequency, a main reason to limit a maximum power application of the product is as following:
A voice coil is likely to be displaced excessively by a high power when operating with the low-frequency. The excessive displacement may cause a significant distortion, even a substantial collision between the voice coil and a magnetic circuit system, such that the loudspeaker will be irreversibly damaged.
Currently, a solution to this problem is to implement an intelligent power amplifier control unit to control and feed back the power of the loudspeaker product. When an vibration displacement of the loudspeaker exceeds a predetermined level, the power are to be decreased. Consequently, the vibration displacement are required to be known. In the prior art, the voice coil of the loudspeaker and an external circuit can be used as a sensor, the monitoring of the vibration displacement of the loudspeaker is realized by the real-time measurement of a loudspeaker model and the real-time monitoring of an input signal. This solution can be carried out provided that the loudspeaker has a theoretical model with reference to the stiffness coefficient Kms of a diaphragm, the mass Mms of a vibration system, the factor of motive power and electricity Bl, the damping factor Rms, the DC resistance Re, the inductance Le, and the like.
However, the theoretical model of the loudspeaker still has some difference with the actual product, leading to limited accuracy on monitoring the displacement of the loudspeaker, such that the low-frequency performance of the loudspeaker is restricted, and the performance optimization of the loudspeaker operating with the low-frequency and the high power is affected.